FIELD
[0001] The present invention relates to an outsole and a shoe including the outsole.
BACKGROUND
[0002] Shoes such as sports shoes conventionally are made up of many members. For example,
a sole is made up of members such as an inner sole, a sock liner, a midsole, and an
outsole. Shoes are required to have functions of not only giving comfortable wearing
feeling to the wearer, but also supporting the wearer's motion, such as running and
stopping. Thus, a conventional shoe has a ground engaging surface provided with projections
and recesses formed into complicated shapes (see Patent Literature 1 below). The outsole
constituting such a ground engaging surface is conventionally composed of an elastomer
sheet such as an uncrosslinked rubber sheet or a crosslinked rubber sheet, in order
to exhibit excellent grip performance.
CITATION LIST
Patent Literature
SUMMARY
Technical Problem
[0004] A shoe with the ground engaging surface having projections and recesses not only
exhibits excellent grip performance against the ground due to the edges of the projections,
but also exhibits excellent grip performance in that the projections are easily deformable
to thereby allow the ground engaging surface to have a relatively large contact area
with the ground. A shoe including an outsole having ridges and grooves arranged alternately
can cause the edges of the ridges to intrude into the recesses of the ground, and
even when protrusions formed, for example, of gravels are present on the ground, each
adjacent ridges of the shoe are forced away from each other allowing the protrusions
to intrude into the groove therebetween, thereby suppressing the ground and the outsole
from being in point contact with each other.
[0005] Usually, the aforementioned effects are remarkably exerted by the projections having
a certain height. However, high projections and deep recesses formed on a shoe sole
may result in a thick shoe sole and thereby result in a heavy shoe. Further, a shoe
provided with a ground engaging surface having deep recesses, into which gravels or
the like are liable to be stuck, may impair its comfortable wearing feeling.
[0006] It is therefore an object of the present invention to provide an outsole helpful
for simplifying the structure of a ground engaging surface and useful for reducing
the weight of a shoe, and to therefore provide a shoe capable of giving a wearer a
feeling of lightness.
Solution to Problem
[0007] In order to solve the above problem, provided in the present invention is an outsole
including at least one elastomer sheet constituting a ground engaging surface, the
at least one elastomer sheet including: a sheet body composed of an elastomer; and
a plurality of polymer particles dispersed in the sheet body, and the plurality of
polymer particles being foamed particles each having a plurality of voids therein.
[0008] Further, in order to solve the above problem, the present invention provides a shoe
including the outsole.
BRIEF DESCRIPTION OF DRAWINGS
[0009]
Fig. 1 is a schematic perspective view showing one form of a shoe.
Fig. 2 is a schematic plan view showing an outsole as viewed from a ground engaging
surface side of the shoe.
DESCRIPTION OF EMBODIMENTS
[0010] The present invention will be hereinafter described by way of embodiments with reference
to the drawings. As shown in Fig. 1, a shoe 1 of this embodiment has an upper material
2, a midsole 3, and an outsole 4.
[0011] The shoe 1 of this embodiment has a shoe center axis Cx connecting an end of a heel
portion HC and an end of a toe portion TC. Hereinafter, the dimension of the shoe
1, a foot, or the like in a direction X along the shoe center axis Cx is referred
to as "length", a direction X1 in the direction X toward the toe is referred to as,
for example, "front", and a direction X2 toward the heel is referred to as, for example,
"rear". Further, hereinafter, a direction Y orthogonal to the length direction X and
parallel to a horizontal plane HP when the shoe 1 is naturally placed on the horizontal
plane HP is referred to as "width direction", and a direction Y1 in the direction
Y toward the medial side of the shoe is referred to as, for example, "inward side",
and a direction Y2 toward the lateral side of the shoe is referred to as, for example,
"outward side". A direction Z orthogonal to the horizontal plane HP is referred to
as "height direction", "vertical direction", or "thickness direction", an ascending
direction Z1 in the direction Z is referred to as, for example, "upper side", and
a descending direction Z2 is referred to as, for example, "lower side".
[0012] As shown in Fig. 2, the shoe 1 of this embodiment has the entire midsole 3 covered
with the outsole 4, as viewed from the side of a ground engaging surface 1a. The outsole
4 of this embodiment is composed of one elastomer sheet 40.
[0013] The elastomer sheet 40 in a substantially horizontal state has an upper side adhering
to a lower side of the midsole 3 and a lower side serving as the ground engaging surface
1a of the shoe. The elastomer sheet 40 includes a plurality of polymer particles that
have been foamed, and the elastomer sheet 40 includes a sheet body 41 and a plurality
of polymer particles 42 dispersed in the sheet body 41. Herein, a description is given
by taking, for example, the case where the outsole 4 is composed of one elastomer
sheet 40, the outsole 4 may be composed of a plurality of elastomer sheets 40. That
is, the outsole 4 is an outsole 4 including at least one elastomer sheet 40 constituting
the ground engaging surface 1a, the at least one elastomer sheet 40 including: the
sheet body 41 composed of an elastomer; and the plurality of polymer particles 42
dispersed in the sheet body 41, the plurality of polymer particles 42 being foamed
particles having a plurality of voids therein.
[0014] In the outsole 4 of this embodiment, mechanical performance characteristics vary
depending on the measurement position since the elastomer sheet 40 includes the polymer
particles 42 and the ground engaging surface 1a has a first area 1a
1 in which the polymer particles 42 are present thereabove and a second area 1a
2 in which no polymer particle 42 is present thereabove. More specifically, in the
outsole 4 of this embodiment, the behavior of compressive deformation of the elastomer
sheet 40 when pressure upward is applied to the ground engaging surface 1a is different
between the first area 1a
1 in which the polymer particles 42 are present and the second area 1a
2 in which no polymer particle 42 is present. In the case where the polymer particles
42 are less elastic than the sheet body 41, the portions in which the polymer particles
42 are present function as if they are recesses of an outsole having an uneven surface.
On the other hand, in the case where the polymer particles 42 are more elastic than
the sheet body 41, the portions in which the polymer particles 42 are present function
as if they are projections of an outsole having an uneven surface. The lower side
of the elastomer sheet 40 of this embodiment is in a substantially flat state although
having a shallow groove 40a slightly recessed upward. The shoe 1 of this embodiment
has the ground engaging portion with no significantly uneven structure, and thus can
be suppressed from having a thick shoe sole resulting from the formation of the uneven
structure. Further, the shoe 1 includes the outsole 4 partially composed of the foamed
polymer particles 42, and thus exerts excellent lightweight properties. The shoe 1
of this embodiment can be easily produced in that the ground engaging surface 1a does
not have an excessively complicated shape.
[0015] It is preferable that the elastomer sheet 40 constituting the outsole 4 have a thickest
part having a thickness of 15 mm or less in order to allow the shoe 1 to exert excellent
lightweight properties. It is more preferable that the thickest part of the elastomer
sheet 40 have a thickness of 10 mm or less. The average thickness of the elastomer
sheet 40 is preferably 10 mm or less, more preferably 8 mm or less. The average thickness
(t (mm)) of the elastomer sheet 40 is determined by dividing the volume (V (cm
3)) of the elastomer sheet 40 by the area (S (cm
2)) of the outline shape of the elastomer sheet 40 obtained by projecting the elastomer
sheet 40 onto the horizontal plane HP (t = V/S). The average thickness (t (mm)) is
usually 1 mm or more.
[0016] The elastomer sheet 40 of this embodiment is configured not to cause the polymer
particles to protrude from its upper or lower surface in order to exert excellent
adhesiveness to the midsole 3 and in order to allow the ground engaging surface 1a
to provide excellent grip performance. Accordingly, in this embodiment, the thickness
of each part of the elastomer sheet 40 is essentially common with the thickness of
the sheet body 41. That is, the sheet body 41 of this embodiment has a thickness of
about 1 to 15 mm.
[0017] The polymer particles 42 are dispersed in this sheet body 41. The polymer particles
42 in this embodiment are mostly uniformly dispersed in the entire outsole. The proportion
of the polymer particles 42 present may differ between the front side and the rear
side of the shoe, or may differ between the inward side and the outward side in the
width direction of the shoe.
[0018] In order to ensure that the polymer particles 42 are present inside the sheet body
41 so that they are not exposed on the surfaces of the elastomer sheet 40, the polymer
particles 42 each preferably have a volume of 100 mm
3 or less at the largest. The average volume of the polymer particles 42 is preferably
75 mm
3 or less per particle, more preferably 65 mm
3 or less per particle. The polymer particles should each have a certain size or larger
to advantageously reduce the weight of the shoe 1. Thus, the average volume of the
polymer particles 42 is preferably 0.5 mm
3 or more per particle, more preferably 1 mm
3 or more per particle. The average volume of the polymer particles can be determined
by, for example, obtaining the respective volumes of 10 to 20 polymer particles 42
randomly selected from the elastomer sheet 40 and arithmetically averaging all the
obtained values of the volumes.
[0019] The proportion of the polymer particles 42 to the elastomer sheet 40 is not particularly
limited, but is preferably 20 volume % or less, more preferably 10 volume % or less,
further preferably 5 volume % or less, most preferably 1 volume % or less, in order
to allow the outsole 4 to exert excellent strength. On the other hand, the proportion
of the polymer particles 42 to the elastomer sheet 40 is not particularly limited,
but is preferably 0.01 volume % or more, more preferably 0.05 volume % or more, in
view of the lightweight properties of the shoe 1.
[0020] It is preferable that the polymer particles 42 in the elastomer sheet 40 be not aggregated
but individually isolated from each other in the sheet body, in order to effectively
exert their function. Specifically, the average value of center-to-center distances
between adjacent polymer particles 42 in the elastomer sheet 40 (i.e., distances in
the horizontal direction: D
1, D
2, D
3...) is preferably 1 mm or more, more preferably 2 mm or more, particularly preferably
5 mm or more. The average value of the center-to-center distances is preferably 30
mm or less, more preferably 25 mm or less.
[0021] It is preferable that the plurality of polymer particles 42 include a small proportion
of polymer particles 42a that are held in contact with each other as shown in Fig.
2 but include a large proportion of isolated particles 42b that are not held in contact
with each other, and that the proportion in the number of the isolated particles 42b
to all the polymer particles 42 in the elastomer sheet 40 be 50% or more. The proportion
in the number of the isolated particles 42b is preferably 60% or more, more preferably
75% or more.
[0022] The proportion in the number and the center-to-center distances of the isolated particles
42b can be measured using the elastomer sheet 40 as it is if, for example, the sheet
body 41 has light permeability and thereby allows the presence of the polymer particles
42 therein to be directly visible from outside, or allows the presence of the polymer
particles 42 to be visible when the sheet body 41 is illuminated with light from a
side thereof and observed from the other side. If the sheet body 41 is opaque and
thus causes the presence of the polymer particles 42 to be hardly visible from outside,
the proportion in the number and the center-to-center distances of the isolated particles
42b can be measured using the elastomer sheet 40 that has been, for example, sliced
at the center in the thickness direction.
[0023] In order to better ensure to produce the elastomer sheet 40 in a preferable condition
as aforementioned, the polymer particles 42 may be interposed between two elastomer
sheets constituting the sheet body 41, followed by hot-pressing, to integrate the
two elastomer sheets with each other. A specific description in this regard will be
given by taking, for example, the case where the sheet body 41 is formed of a thermoplastic
elastomer. The elastomer sheet 40 can be produced by: preparing two thermoplastic
elastomer sheets each having an area larger than that of the elastomer sheet 40; interposing
the polymer particles between these sheets to produce a laminated body; cutting out
a preliminarily molded product having a shape corresponding to that of the elastomer
sheet 40 from the laminated body; placing the preliminarily molded product in a forming
mold constituted by a male mold and a female mold that form an internal space corresponding
to the shape of the elastomer sheet 40 when the mold is closed; and hot-pressing the
preliminarily molded product at temperature conditions at which the thermoplastic
elastomer is heat-sealed.
[0024] A similar hot-pressing method can be applied also in the case where a crosslinked
rubber sheet is used as the sheet body 41. That is, the elastomer sheet 40 can be
produced by: preparing two uncrosslinked rubber sheets larger than the elastomer sheet
40; interposing the polymer particles between these sheets to produce a laminated
body; cutting out a preliminarily molded product having a shape corresponding to that
of the elastomer sheet 40 from the laminated body; placing the preliminarily molded
product in the molding space; and applying pressure to the preliminarily molded product
using the male mold and the female mold at temperature conditions at which the two
uncrosslinked rubber sheets are crosslinked and integrated together.
[0025] The sheet body is preferably formed of a crosslinked rubber to allow the outsole
4 to have excellent abrasion resistance. At the time of crosslinking a rubber, there
are some cases where the rubber partially turns into a sponge-like form to thereby
fail to exert sufficient strength unless a relatively high pressure is generated in
the mold. In order to ensure that the sheet body is in a non-foamed state to be clearly
distinguished from the polymer particles 42 in terms of their behavior under compressive
deformation, it is preferable to perform the hot-pressing under high pressure. However,
there is a possibility that the polymer particles 42 are crushed to thereby decrease
their degree of foaming or partially turn into a non-foamed state if the pressing
is performed under high pressure when producing the elastomer sheet 40. For the purpose
of avoiding this possibility, foamed particles each having a plurality of voids therein
are employed as the polymer particles 42 in this embodiment rather than balloon-shaped
foamed particles each having only one internal void, and in terms of the abovementioned,
it is preferable to employ foamed particles having excellent heat resistance as the
polymer particles 42. It is preferable to employ those composed of a thermoplastic
elastomer as the polymer particles 42. Among the thermoplastic elastomers, formed
particles composed of a polyurethane-based thermoplastic elastomer (TPU) are preferable
as the polymer particles 42 in that they are excellent in heat resistance and abrasion
resistance. The polyurethane-based thermoplastic elastomer (TPU) forming the polymer
particles 42 is preferable, for example, in that it has a molecular structure including
a polyol-derived first structural unit and a polyisocyanate-derived second structural
unit and that the elastomer having a polyether polyol-derived structural unit as the
first structural unit is excellent in hydrolysis resistance.
[0026] The polymer particles 42 are preferably foamed in advance of producing the elastomer
sheet 40, but for the purpose of preventing the polymer particles 42 from being crushed
in the course of producing the elastomer sheet 40, it is preferable that the polymer
particles 42 have their foaming power remaining. That is, it is preferable that a
foam agent included in the polymer particles 42 be used for turning the polymer particles
42 into a foamed state in advance but partially remain unused, and allow the polymer
particles 42 to exert their foaming power at the time of the production of the elastomer
sheet 40. The polymer particles 42 used for producing the elastomer sheet 40 preferably
include, for example, 0.1 mass % to 3 mass % of a physical foam agent such as hydrocarbon.
[0027] The polymer particles 42 may be coated with other polymers and dispersed in the sheet
body for the purpose of achieving improved adhesiveness to the sheet body 41 or making
them difficult to be deformed by external forces. The coating applied to the polymer
particles 42 primarily for the former purpose can be performed, for example, using
a coating agent including an adhesive component such as rosin, a silane coupling agent,
or the like. The coating applied to the polymer particles 42 primarily for the latter
purpose can be performed, for example, using a coating agent including a hard resin
such as an epoxy resin, an inorganic filler, or the like.
[0028] The polymer particles 42 of this embodiment are preferably formed of a polymer composition
including a polyurethane-based thermoplastic elastomer as described above, but may
be composed of a composition other than such a polymer composition. The polymer particles
42 may be composed of a polymer composition including, for example, one or more of
a polyurethane-based thermoplastic elastomer (TPU), polyethylene (PE), polypropylene
(PP), an ethylene-vinyl acetate copolymer (EVA), a polyamide-based elastomer (PA),
polyether block amide (PEBA), polystyrene (PS), polyoxymethylene (POM), polyoxyethylene
(POE) and a polyester-based elastomer (PET, PBT). The polymer composition forming
the polymer particles 42 may be selected appropriately based on thermal resistance
and abrasion resistance required for the outsole, and affinity for the elastomer constituting
the sheet body 41. For example, in the case where excellent heat resistance is required
for the outsole 4, the polymer constituting the polymer particles 42 may suitably
include one or more of a polyurethane-based thermoplastic elastomer, polypropylene,
a polyamide-based elastomer, polyether block amide, and a polyester-based elastomer.
[0029] The elastomer constituting the sheet body 41 may be any elastomer suitable as an
elastomer constituting the ground engaging surface of an outsole, such as a crosslinked
rubber or a thermoplastic elastomer. The elastomer constituting the sheet body 41
can be appropriately selected based on hardness, durability, or the like required
for the outsole. For example, in the case where the outsole 4 is an outsole for running
shoes, the shore A hardness of the elastomer constituting the sheet body 41 is preferably
40 to 90.
[0030] Conventionally known materials can be used for the members other than the outsole
that constitute the shoe 1, such as the upper member 2 and the midsole 3. The shoe
1 provided with the aforementioned outsole 4 exerts excellent lightweight properties
to thereby effectively give the wearer a feeling of lightness.
[0031] The outsole and shoe according to the present invention is not limited to the abovementioned
embodiment, but various modifications can be made without departing from the gist
of the present invention.
[0032] For example, in the outsole according to the present invention, the polymer particles
dispersed in the sheet body may not necessarily be uniformly dispersed in the entire
outsole. For example, the polymer particles may concentrate in a certain portion of
an outsole, such as a heel portion or a forefoot portion of the outsole. In the case
where the polymer particles concentrate in a certain portion of an outsole as described
above, the mechanical performance characteristics in a desired portion of the outsole
can be effectively adjusted.
REFERENCE SIGNS LIST
[0033]
1: Shoe
2: Upper sole
3: Midsole
4: Outsole
40: Elastomer sheet
41: Sheet body
42: Polymer particle
42b: Isolated particle